The Stovebolt Site Forums The Shop Area Engine Shop I.D'ing my rear axle/differential-pics linked

Newbie here. I love this forum. Spent the last 4 days drooling over all the information. Waded through a ton of posts on differentials and gleaned some information regarding my rear axle/differential, but I have a few more steps to fully convince myself what I have.
The Reader's Digest version: I 'obtained' this truck 20 years ago and drove it for several years. It's a '59 Apache 3100 with the original 235 and 3 spd column shift. The truck has stayed with me (only idle) and now my youngest son and I are returning the old girl back to the street.
Everything leaks.
To keep his brakes safe, the rear axle needs new seals. We opened up the diff and removed the right side axle. It has a 17 spline axle and 6 lugs for the wheel. The part of the axle that rides on the outboard wheel bearing is 1.875" diameter.
The differential has 39 teeth on the ring gear and 10 on the pinion gear. I suspect I have a 3.90 ratio diff.
The teeth on the ring gear are showing some scoring and the spider gears have some bad pitting.
When we pulled the right axle, we found a piece of what looks like a ring gear tooth inside the axle. **This is not from the current ring gear!** There is a mark on the rear cover that appears to have been caused by an earlier catastrophic event. (before I owned the truck)
So- to make a long post even longer;
1)What model rear axle/differential do I have?
2) How available will new replacements parts be to find?

Thanks

Chris

Got a pic? Most likely, it will be the std Eaton suppkied diff used from '55-'62 (some '63s used it too). S far as parts go, all of the seals and the crush sleeve are still avalable, gears are iffy. I know that there is a 3.38 gear set, but it can be difficult to get depending on production. Spiders are not available, either. I do know of a company, Tom's differentials, that makes replacement axles that convert it to the a 30 spline, allowing the use of '65 and later 12 bolt spiders. Most likely, though, if you want to stay with the original gear ratio and axles, used is about the only way you're going to find them.

Thanks Bill,
Yes, I have a couple of pictures that I took last night, but after reading more today, I need to take another picture of the right side of the front pinion housing (dropout?) I will post all the pictures tonight when I get home.
I neglected to mention that the rear cover has 10 bolts and the front cover also has 10 bolts. It looks as though I can take out the front pinion support(?)
I should also count the bolts on the ring gear I guess. This information might make it easier to identify. I was looking for markings/ numbers on the left side, but I believe I might find what I'm looking for on the right side.
Right now I'm in search of the axle seals, and as always- my first trip to the local autoparts store ended with me ordering seals that don't fit. Fortunately, we pulled the old seal out of the right side and 'National 5801' was stamped on the old seal face. I am trying to cross-reference this old part now.
More later- I'll post some pictures.

Chris

This is the diff in mine, the clean area is where the coding is stamped. http://rides.webshots.com/photo/2207314170092261295jzkmtK

OK, I've got some pictures uploaded to the web. Let me know if this works out.
My diff looks like it has the stamp 'AF105' on it.
See what you make of it.
http://picasaweb.google.com/chris.happ/59Chevy

AF-3.90 gear ratio, 10 5- 10th day, 5th month. It is the std Eaton sorced diff, 10 bolt cover, 12 bolt 9.375" ring gear. Not to hard to get seals and gaskets for. Not bad to work on either.

LONGBOX55

Do you know if there was another ratio produced by Chevy for those differentials, possibly a 3.38. Or is that strictly an aftermarket kit. If the 3.38 was a factory option do you know the stamped code? It would save me a lot of time jacking up old bone yard trucks to spin the tires.

Yes, 3.38 was an option. the codes are AY, MB, ME.

Well, we've disassembled, cleaned, painted and installed new seals. I was hoping to be able to adjust the lash between the pinion and ring gears out since the bearings all appear to be in good shape. Unfortunately, it does not seem to be the case. The gears or the bearings have just enough slop in them that when I adjust the lash to zero, the whloe thing locks up pretty tight.
I will post pictures this week of how the diff looks with new paint, along with seal numbers for anyone looking to find replacement parts for a similar rear diff/axle.
The next question: Where can new gears and bearing sets be found for these? I've waded through Rick's ringpinion.com, but can't seem to get past all the available positraction setups.

I found them quickly using a simple Google search for Randy's Ring & Pinion @ www.ringpinion.com

Install kits, bearings, tools, gears in both 3:90 and 3:38 available. They show this as a GM T55 rear.